This is a continuation-in-part of United States patent application Ser. No. 06/080,153 filed Sept. 28, 1979, now U.S. Pat. No. 4,284,957 and assigned to American Microsystems, Inc., 3800 Homestead Road, Santa Clara, Calif. 95051. This invention relates to operational amplifiers and more particularly, to such devices that may be utilized as building blocks in integrated circuits.
In the development of data transmission and communication systems, efforts have been made to utilize linear integrated circuit devices, such as those incorporating complementary metal-oxide-silicon (CMOS) large scale integrated (LSI) technology. Operational amplifiers are key building blocks in many circuits used for such systems. However, with previous operational amplifiers comprised of integrated MOSFET elements, excessive power dissipation and limited available open loop gain were problems that limited their use, particularly, where relatively large numbers of such circuits were required for system operation. Previous conventional operational amplifiers using CMOS LSI technology were designed with a constant bias drive for the output stage. This factor contributed to the problem of excessive power requirements and also, limited loop gain.
It is, therefore, one object of the invention to provide an improved operational amplifier circuit that solves the aforesaid problems and provides for relatively low power dissipation.
Another object of the present invention, is to provide an operational amplifier that produces an increased gain factor over comparable circuits using constant bias drive for the output stage.
Another object of the present invention, is to provide an operational amplifier that has an increased linear signal swing range compared to what was previously achievable with an operational amplifier having a constant bias for the output stage.
Yet another object of the present invention, is to provide an operational amplifier comprised of CMOS MOSFET elements which provide relatively low power dissipation and increased open loop gain.
Another object of this invention is to provide an operational amplifier having a low output impedance.